Methods of forming an insulating material proximate a substrate, and methods of forming an insulating material between components of an integrated circuit

ABSTRACT

In one aspect, the invention encompasses a method of forming an insulating material around a conductive component. A first material is chemical vapor deposited over and around a conductive component. Cavities are formed within the first material. After the cavities are formed, at least some of the first material is transformed into an insulative second material. In another aspect, the invention encompasses a method of forming an insulating material. Polysilicon is deposited proximate a substrate. A porosity of the polysilicon is increased. After the porosity is increased, at least some of the polysilicon is transformed into silicon dioxide.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a Continuation Application of U.S. patentapplication Ser. No. 08/948,372, filed on Oct. 9, 1997, entitled“Methods Of Forming An Insulating Material Proximate A Substrate, AndMethods Of Forming An Insulating Material Between Components Of AnIntegrated Circuit”, naming Leonard Forbes and Kie Y. Ahn as inventors,now U.S. Pat. No. 6,251,470, the disclosure of which is herebyincorporated herein by reference.

TECHNICAL FIELD

The invention pertains to methods of forming insulating material, suchas for example, methods of forming insulating material betweencomponents of integrated circuits.

BACKGROUND OF THE INVENTION

In methods of forming integrated circuits, it is frequently desired toisolate components of the integrated circuits from one another withinsulative material. Such insulative material may comprise a number ofmaterials, including, for example, silicon dioxide, silicon nitride, andundoped semiconductive material, such as silicon. Although suchmaterials have acceptable insulative properties in many applications,the materials disadvantageously have high dielectric constants which canlead to capacitive coupling between proximate conductive elements. Forinstance, silicon dioxide has a dielectric constant of about 4, siliconnitride has a dielectric constant of about 8, and undoped silicon has adielectric constant of about 12.

It would be desirable to develop alternative methods for insulatingconductive elements from one another with low-dielectric-constantmaterials.

SUMMARY OF THE INVENTION

The invention encompasses methods of forming insulating materialsproximate conductive elements.

In one aspect, the invention encompasses a method of forming aninsulating material proximate a substrate in which a first material ischemical vapor deposited proximate the substrate. Cavities are formedwithin the first material, and, after forming the cavities, at leastsome of the first material is transformed into an insulative secondmaterial.

In another aspect, the invention encompasses a method of forming aninsulating material proximate a substrate in which porous polysilicon isformed proximate the substrate and at least some of the porouspolysilicon is transformed into porous silicon dioxide.

In yet another aspect, the invention encompasses a method of forming aninsulating material between components of an integrated circuit.Polysilicon is chemical vapor deposited between two components andelectrochemically anodized to convert the polysilicon into a porous masshaving a first volume. The first volume comprises a polysilicon volumeand a cavity volume, with the cavity volume comprising greater than orequal to about 75% of the first volume. The porous polysilicon mass isoxidized to transform the polysilicon into porous silicon dioxide havinga second volume. The second volume comprises a silicon dioxide volumeand a cavity volume, with the cavity volume comprising less than orequal to about 50% of said second volume.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic cross-sectional view of a semiconductor waferfragment at a preliminary step of a processing method of the presentinvention.

FIG. 2 is a view of the FIG. 1 wafer fragment shown at a processing stepsubsequent to that of FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment shown at a processing stepsubsequent to that of FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment shown at a processing stepsubsequent to that of FIG. 3.

FIG. 5 is a view of the FIG. 4 wafer fragment shown at a processing stepsubsequent to that of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

FIG. 1 shows a semiconductive wafer fragment 10 at a preliminaryprocessing step of the present invention. Wafer fragment 10 comprises asubstrate 12 and conductive elements 14 and 16 overlying substrate 12.Substrate 12 may comprise, for example, a monocrystalline silicon wafer.To aid in interpretation of the claims that follow, the term“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove.

Conductive elements 14 and 16 may comprise, for example, conductivelines. Conductive elements 14 and 16 might be part of an integratedcircuit, for example. Although conductive elements 14 and 16 areillustrated as being horizontally displaced, such elements could also bedisplaced along a non-horizontal axis. For example, such elements couldbe vertically displaced from one another.

An insulative material 18 is formed between substrate 12 and conductiveelements 14 and 16. Insulative material 18 can comprise a number ofmaterials known to persons of ordinary skill in the art, such as, forexample, silicon nitride and silicon dioxide. Insulative material 18 isprovided to electrically isolate conductive elements 14 and 16 fromsubstrate 12. Such electrical isolation might be desired, for example,if substrate 12 is conductive or semiconductive.

Referring to FIG. 2, a first material 20 is deposited proximatesubstrate 12 and between conductive elements 14 and 16. First material20 preferably comprises polysilicon, and is preferably formed bychemical vapor depositing. Methods for chemical vapor depositingpolysilicon are known to persons of ordinary skill in the art, andinclude, for example, methods comprising thermal decomposition ofsilane.

Referring to FIG. 3, cavities 22 are formed within first material 20.The formation of cavities 22 within first material 20 converts firstmaterial 20 into a porous first material. In a preferred example inwhich first material 20 comprises polysilicon, cavities 22 may be formedby, for example, either electrochemical anodization or by subjecting thepolysilicon to a chemical etch. An example method of electrochemicalanodization comprises doping preferred polysilicon layer 20 and makingwafer fragment 10 an anode in an aqueous hydrofluoric acid solution. Thehydrofluoric acid solution can comprise, for example, 20 wt. % HF, andthe amount of current applied with wafer fragment 10 as anode cancomprise, for example, about 10 mA for a 100 mm diameter wafer. Anexample method of chemical etching comprises doping preferredpolysilicon layer 20 with a p-type conductivity-enhancing dopant andsubsequently chemically etching layer 20 with a phosphoric acidsolution.

Preferably, greater than about 50% of a volume of layer 20 will beremoved in forming cavities 22. More preferably, at least about 75% of avolume of layer 20 will be removed in forming cavities 22. In otherwords, the formation of cavities 22 converts the first material of layer20 into a porous mass having a first volume which comprises apolysilicon volume and a cavity volume, wherein the cavity volume ismost preferably greater than or equal to about 75% of the first volume.

Referring to FIG. 4, first material 20 (shown in FIG. 3) is transformedinto an insulative second material 30. Where the first material 20comprise s polysilicon, such transformation can occur, for example, byoxidizing polysilicon layer 20 to transform such polysilicon layer to asilicon dioxide layer 30. Methods for oxidizing a polysilicon layer areknown to persons of ordinary skill in the art, and include, for example,thermal oxidation utilizing one or more of the oxygen-containingcompounds O₂, O₃ and H₂O. In the shown embodiment, substantially all offirst material 20 is transformed into insulative second material 30.However, it is to be understood that the invention also encompassesembodiments in which only some of first material 20 is transformed intoinsulative second material 30. In the shown preferred embodiment,oxidation of polysilicon layer 20 (shown in FIG. 3) having a firstvolume swells the layer into a silicon dioxide layer 30 having a secondvolume which is larger than the first volume. The increase in volume oflayer 30 relative to layer 20 changes the relative volume occupied bycavities 22. For instance, in an example embodiment in which cavities 22comprise a cavity volume greater than or equal to about 75% of a firstvolume of porous polysilicon layer 20 (shown in FIG. 3), the cavityvolume can comprise less than or equal to about 50% of a volume ofporous silicon dioxide layer 30 formed by oxidizing such layer 20.

The cavities 22 within second material layer 30 lower a dielectricconstant of the material relative to what the dielectric constant wouldbe in the absence of cavities 22. Cavities 22 will preferably be filledwith some gas. Gases typically have a dielectric constant of about 1,which is less than a dielectric constant of most commonly usedinsulative materials. For instance, if the insulative solid material oflayer 30 comprises silicon dioxide, the silicon dioxide will typicallyhave a dielectric constant of about 4. The addition of cavities 22within material layer 30 decreases the dielectric constant of thematerial 30 to less than 4. In the above-described embodiment in whichcavities 22 comprise about 50% of the total volume of layer 30, and inwhich layer 30 comprises silicon dioxide, layer 30 can have a dielectricconstant of about 1.6. Accordingly, the method of the present inventioncan form a porous silicon dioxide insulative layer having a dielectricconstant of less than or equal to about 1.6.

As shown in FIG. 5, layer 30 can be utilized to support additionalcircuitry formed over conductive elements 14 and 16. In the shownembodiment, a filling layer 32 is provided over layer 30. Filling layer32 can comprises any of a number of materials known to persons ofordinary skill in the art, including, for example, insulative materialssuch as silicon dioxide or silicon nitride. Filling layer 32 can beprovided by, for example, chemical vapor deposition. Filling layer 32 isplanarized, such as, for example, by chemical-mechanical polishing, toform a substantially planar upper surface 34.

After forming a planar upper surface 34 over layer 30, circuit elements40, 42 and 44 are formed over the upper surface. Circuit elements 40, 42and 44 can be formed by conventional methods.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of forming an insulating materialproximate a substrate comprising: forming polysilicon proximate asubstrate; forming cavities within the polysilicon to enhance porosityof the polysilicon; and after forming the cavities, transforming atleast some of the polysilicon into porous silicon dioxide.
 2. The methodof claim 1 further comprising forming at least one structure over theporous silicon dioxide.
 3. The method of claim 1 wherein the poroussilicon dioxide comprises a volume, wherein the cavities comprise acavity volume, and wherein the cavity volume is less than or equal toabout 50% of the volume of the porous silicon dioxide.
 4. The method ofclaim 1 wherein the formed polysilicon has a first volume before formingcavities, and wherein the forming cavities removes greater than about50% of said first volume of the formed polysilicon.
 5. The method ofclaim 1 wherein the forming polysilicon comprises chemical vapordeposition.
 6. The method of claim 1 wherein the forming cavitiescomprises electrochemical anodization.
 7. The method of claim 1 whereinthe forming cavities comprises subjecting the polysilicon to a chemicaletch.
 8. The method of claim 1 wherein the forming cavities comprises:doping the polysilicon with a p-type dopant; and subjecting the dopedpolysilicon to a phosphoric acid etch.
 9. The method of claim 1 whereinthe porous silicon dioxide comprises a dielectric constant of less than4.
 10. The method of claim 1 wherein the porous silicon dioxidecomprises a dielectric constant of less than or equal to about 1.6. 11.The method of claim 1 wherein transforming comprises transforming all ofthe polysilicon into porous silicon dioxide.
 12. A method of forming aninsulating material proximate a substrate comprising: forming asemiconductive material proximate a substrate; forming cavities withinthe semiconductive material to enhance porosity of the semiconductivematerial; and after forming the cavities, transforming at least some ofthe semiconductive material into porous dielectric material, whereinforming semiconductive material comprises chemical vapor deposition ofpolysilicon.
 13. The method of claim 12 further comprising forming atleast one structure over the porous dielectric material.
 14. The methodof claim 12 wherein the porous dielectric material comprises poroussilicon dioxide and the porous silicon dioxide comprises a volume,wherein the cavities comprise a cavity volume, and wherein the cavityvolume is less than or equal to about 50% of the volume of the poroussilicon dioxide.
 15. The method of claim 12 wherein the formedsemiconductive material has a first volume before forming cavities, andwherein the forming cavities removes greater than about 50% of saidfirst volume of the formed semiconductive material.
 16. The method ofclaim 12 wherein forming cavities comprises electrochemical anodization.17. The method of claim 12 wherein forming cavities comprises subjectingthe semiconductive material to a chemical etch.
 18. The method of claim12 wherein forming cavities comprises: doping the polysilicon with ap-type dopant; and subjecting the doped polysilicon to a phosphoric acidetch.
 19. The method of claim 12 wherein the porous dielectric materialcomprises porous silicon dioxide having a dielectric constant of lessthan
 4. 20. The method of claim 12 wherein the porous dielectricmaterial comprises porous silicon dioxide having a dielectric constantof less than or equal to about 1.6.
 21. The method of claim 12 whereintransforming comprises transforming all of the semiconductive materialinto porous silicon dioxide.
 22. A method of forming an insulatingmaterial, comprising: forming polysilicon proximate a silicon substrate;forming cavities within the polysilicon to enhance porosity of thepolysilicon; after forming the cavities, transforming the polysiliconinto porous silicon dioxide; and forming at least one structure over theporous silicon dioxide.